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Top1. Introduction
Alum sludge is produced in huge quantities in water plants using Al salts as flocculants and it impose heavy burden on the environment and difficulties in its disposal. One technique to decrease the volume of sludge is dewatering it to smooth partial separation of its water. In this situation the conditioned sludge will have smaller volume with low moisture content that will results in smaller volume of land required for sludge disposal by landfilling. However further release of the environment burden will be satisfied if this conditioned sludge could be recycled in a way or another (Dassanayake et al.2015).
Techniques of Alum Sludge conditioning involve treating it with chemicals and mechanical dewatering. Used chemicals include alum, iron chloride and iron sulfate. Other alternatives have been utilized for sludge conditioning including Fenton’s reaction, pH, adjustment, and freezing-thawing (Zhang et al.2012, Lee et al. 2014 and Yang et al. 2015).
Previous studies showed that conditioning sludge with inorganic chemicals, organic chemicals, or thermal treatrnent resulted in a sludge of inferior qualities with respect to lower value for Specific Resistance for Filtration (SRF), higher percentage reduction in the values of SRF compared to the raw sludge and lower values for the turbidity of effluents resulting from sludge filtration (Capodici et al. 2016).
On the other hand, spreading of chemical industries has resulted in environmental pollution that has become an important environmental matter. The textile process is an important industrial sector that disposes of a large amount of highly polluted wastewater (Jegatheesan et al 2016). Huge amount of dyes are produced from the textile industries in the same time high percentage of them are discharged in their effluents to the global environment annually. Dye wastewater contains a number of pollutants including acids, bases, dissolved and suspended solids and non-biodegradable compounds, which are remarkably, even at low concentrations, should be removed or decolorized before the wastewater is discharged to environment (Bazrafshan et al 2014). Conventional physico-chemical treatments applied to purify the dyeing wastewaters include adsorption with inorganic and organic materials, ion exchange, precipitation, filtration and coagulation, but their major drawback is the formation of sludge (Mojsov 2016 and Mustapha et al. 2015). Different water treatment processes produce large amounts of alum sludge where immediate attention has be directed to satisfy economic sustainability and environmental management. Sludge produced from drinking water treatment processes is estimated to be about 100,000 ton/year of sludge through the treatment process. Alum sludge is produced from drinking water purification units when aluminum (Al) salts are added as the primary coagulating–flocculating agents (Ahmad et al. 2016). The proper disposal or reuse of waste sludge has become an interesting environmental issue. Sludge employment has become the most important method for sludge disposal (Dassanayake et al. 2015). It was reported that when using alum generated sludge to remediate ammonium-rich wastewater; ammonium alum with high percentage recovery was obtained (Cheng et al.2016). Thus, sludge with large mesoporosity and cation exchange capacity has been utilized as an adsorbent, a cheaper substitute for activated carbon. The latter has proved to be an efficient adsorbent and it has extensive applications in adsorbing several heavy metals, organic compounds, dyes and gaseous contaminants (Bian et al. 2018, Hadi et al 2015 and Xu et al.2015).